This invention relates to a method for monitoring the accurate and proper sequential order of successive code signal groups, e.g., binary numbers having a prespecified length such as address and/or instruction words in program-controlled information processing equipments.
Generally, code signal groups are employed to represent intelligence signals or information words. In many cases, in order to be able to verify the validity of code signal groups check characters (e.g., parity bits) in the form of binary numbers are added to each code signal group.
Frequently, the correct sequence of such code signal groups is also of prime importance. For this reason, it is a known practice for purposes of communication to combine code signal groups into blocks and to assign thereto within the block ordinal numbers indicating the sequence. However, this technique is only appropriate if the number of code signal groups within a block is comparatively small. If a multiplicity of code signal groups are present in a sequence, this technique involves greater system complexity.
An arrangement is known from U.S. Pat. No. 3,192,362 wherein the proper sequential operation of an instruction address counter in a program-controlled data processing unit is so monitored that the parity of the address waiting for service and the stored parity of the preceding address are compared with each other, and the values of corresponding bits in both addresses are fixed and checked in accordance with a predetermined logic. The validity of the address sequence is then deduced from these checks. In most caes, such a method is much too complicated.
An improved method is described in British Pat. No. 1,038,704, wherein each code signal group has two additional parity bits, one of which is derived from the address of the subsequent code signal group and the other from the address associated with the code signal group in question. During the readout of a code signal group the check character derived from the subsequent code signal group is buffered until the readout of the subsequent code signal group, and it is then compared with the other check character. If the two check characters being compared do not agree, an error signal is generated.
Accordingly, it is an object of this invention to provide a method that enables in a simple way and with little further expenditure and system complexity the monitoring of the code signal groups for insuring the accurate and proper sequential order of retrieval of information in a stored program machine or the like.